The use of wireless communication devices such as telephones, pagers, personal digital assistants, laptop computers, etc., hereinafter referred to collectively as mobile devices, mobile appliances or wireless devices, has become prevalent in today's society. At the urging of public safety groups, there is an interest in technology which can determine the geographic position or “geo-location” of a mobile appliance in certain circumstances. For example, the Federal Communication Commission (“FCC”) issued a geo-location mandate for providers of wireless telephone communication services that puts in place a schedule and an accuracy standard under which the providers of wireless communications must implement geo-location technology for wireless telephones when used to make a 911 emergency (“E911”) telephone call.
In addition to E911 emergency related issues, wireless telecommunications providers are developing location-enabled services for their subscribers including roadside assistance, turn-by-turn driving directions, concierge services, location-specific billing rates and location-specific advertising. To support FCC E911 rules to locate wireless 911 callers, as well as the location-enabled services, the providers of wireless communication services are installing mobile appliance location capabilities into their networks. In operation, these network overlay location systems take measurements on radio frequency (“RF”) transmissions from mobile appliances at base station locations surrounding the mobile appliance, and estimate the location of the mobile appliance with respect to the base stations. Because the geographic location of the base stations is known, the determination of the location of the mobile appliance with respect to the base station permits the geographic location of the mobile appliance to be determined. The RF measurements of the transmitted signal at the base stations may include, but are not limited to, time difference of arrival (“TDOA”), time of arrival (“TOA”), angle of arrival (“AOA”), signal power, unique/repeatable radio propagation path (radio fingerprinting) derivable features, etc. In addition, geo-location systems may also use collateral information, e.g., information other than that derived for the RF measurement to assist in the geo-location of the mobile appliance, for example, location of roads, dead-reckoning, topography, map matching, etc.
In a network-based geo-location system, the mobile appliance to be located is typically identified and radio channel assignments determined by (a) monitoring the control information transmitted on a radio channel or wireline interface that is part of the wireless communication system for telephone calls being placed by the mobile appliance to detect calls of interest, e.g., 911 calls, (b) a location request provided by a non-mobile appliance source, e.g., an enhanced services provider. Once a mobile appliance to be located has been identified and radio channel assignments determined, the location determining system is first tasked to determine the geo-location of the mobile appliance. Then the location determining system may be directed to report the determined position to a requesting entity or enhanced services provider.
The monitoring of RF transmissions from the mobile appliance or wireline interfaces containing call setup or channel assignment information to identify calls of interest is known as “tipping” and generally involves recognizing a call of interest being made from a mobile appliance and collecting the call setup information. Once the mobile appliance is identified and the call setup information collected, the location determining system can be tasked to geo-locate the mobile appliance.
FIG. 1 is a block diagram of a typical geo-location process 100. In the normal course of operation, a Geolocation Control Station (“GCS”) may be tasked by an outside entity to generate a location estimate on a particular mobile appliance in block 110. The tasking typically is accompanied by information on the mobile of interest which may include the serving base station and sector for the call and the RF channel (frequency, time slot, Code Division Multiple Access (“CDMA”) code, etc.) being used by the wireless communications network to complete the wireless connection. Once the GCS receives this tasking, it may task Location Measurement Units (“LMU”) proximate to the serving sector or serving base station to detect the signal from the target mobile appliance in block 120. The LMUs may determine measurements on the RF emissions of the mobile appliance's signal, as indicated by block 130. The LMUs may then report the measurements to the GCS. The GCS then computes a location estimate typically using some mathematical or data matching algorithm, as represented in block 140, and reports the estimated location to the requesting entity, as indicated in block 150. Control channels/information on either RF or wireline links may also be utilized to set up calls in the wireless network can be scanned to detect the placement of a call of interest. The signaling that occurs on the control channel may be used to determine location. Further, RF traffic channel parameters may be extracted from the control channel messaging to determine which traffic channel to use for location related measurements.
Network overly location systems typically locate a mobile appliance on the traffic channels of a wireless network using sensors employing various techniques of TDOA, AOA, TOA and other techniques. Geo-location systems, when not being tasked to locate a mobile appliance for emergency or other location-based services, are effectively in an idle mode. The tasking duty cycle may vary depending on what uses are being made of the location data. For E911 purposes, the effective utilization of the location network is low. With other location enabled value added services, the use may be higher, depending upon the service. For example, a service providing turn-by-turn instructions to a motorist would likely be higher than a service that provides road side assistance.
Typical location processes may commence after receipt of tipping information. Samples are generally collected according to the tipping information and then data bits are demodulated at a primary site and sent to the secondary sites through the GCS. This process occurs over the course of several seconds and the collection of data and exchange of demodulated bits incur a large overhead in this typical geo-location process. The performance of any correlation is relatively small in comparison to other overheads and the location process may be accelerated or improved if the collection time is reduced and the exchange of demodulated bits eliminated.
Thus, there is a need in the art to overcome the limitations of the prior art and provide a novel system and method for a high throughput GSM location solution. It is therefore an object of embodiments of the present subject matter to provide a locator system capable of locating tens of mobile calls per second and/or locate mobile devices, active or otherwise, at any given instant.
One embodiment of the present subject matter provides a method for estimating a location of wireless devices transmitting signals on channels in a communications system having a plurality of nodes and a plurality of LMUs. The method may include receiving a first plurality of signals from a first channel by one or more of the plural LMUs and receiving a second plurality of signals from a second channel by one or more of the plural LMUs. The received first and second plural signals may be converted into first and second digital signals and divided into first and second sets of frequency bins, the first and second sets of bins corresponding to the respective channel. Each of the divided signals may be correlated with one or more reference signals and stored in a database for estimating a location of one or more wireless devices.
Another embodiment of the present subject matter provides a method for estimating a location of a wireless device in a communication system having a plurality of nodes and a plurality of LMUs. Tipping information may be received by ones of the plural LMUs, the tipping information corresponding to the wireless device, and the wireless device may be located as a function of signals transmitted from the wireless device prior to receipt of the tipping information.
A further embodiment of the present subject matter provides a method for estimating a location of a wireless device transmitting signals on a channel in a communication system having a plurality of nodes and a plurality of LMUs. Tipping information may be received by ones of the plural LMUs, the tipping information corresponding to the wireless device, and the wireless device may be located as a function of the tipping information after the device is no longer transmitting signals.
These embodiments and many other objects and advantages thereof will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the embodiments.